linux-kernel - Re: [PATCH v1 3/3] perf-security: document perf

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Message-ID: <20190206170151.00c92333@lwn.net>
Date:   Wed, 6 Feb 2019 17:01:51 -0700
From:   Jonathan Corbet <corbet@....net>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Jann Horn <jannh@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Andi Kleen <ak@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/3] perf-security: document perf_events/Perf
 resource control

On Fri, 1 Feb 2019 10:30:58 +0300
Alexey Budankov <alexey.budankov@...ux.intel.com> wrote:

> Elaborate on possible perf_event/Perf privileged users groups
> and document steps about creating such groups.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
>  Documentation/admin-guide/perf-security.rst | 43 +++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst
> index 7da7fa459718..fe90f8952be9 100644
> --- a/Documentation/admin-guide/perf-security.rst
> +++ b/Documentation/admin-guide/perf-security.rst
> @@ -73,6 +73,48 @@ enable capturing of additional data required for later performance analysis of
>  monitored processes or a system. For example, CAP_SYSLOG capability permits
>  reading kernel space memory addresses from /proc/kallsyms file.
>  
> +perf_events/Perf privileged users
> +---------------------------------
> +
> +Mechanisms of capabilities, privileged capability-dumb files [6]_ and file system
> +ACLs [10]_ can be used to create a dedicated group of perf_events/Perf privileged
> +users who are permitted to execute performance monitoring without *scope* limits.
> +The following steps can be taken to create such a group of privileged Perf users.
> +
> +1. Create perf_users group of privileged Perf users, assign perf_users group to
> +   Perf tool executable and limit *access* to the executable for other users in
> +   the system:
> +
> +::
> +
> +   # groupadd perf_users
> +   # ls -alhF
> +   -rwxr-xr-x  2 root root  11M Oct 19 15:12 perf
> +   # chgrp perf_users perf
> +   # ls -alhF
> +   -rwxr-xr-x  2 root perf_users  11M Oct 19 15:12 perf
> +   # chmod o-rwx perf
> +   # ls -alhF
> +   -rwxr-x---  2 root perf_users  11M Oct 19 15:12 perf

Since we're giving basic sysadmin info here, we should probably say
explicitly that this will block access to the perf binary to anybody who
is not in the perf_users group.

> +2. Assign required capabilities to the Perf tool executable file and enable

Assign *the* required

> +   members of perf_users group with performance monitoring privileges [6]_ :
> +
> +::
> +
> +   # setcap "cap_sys_admin,cap_sys_ptrace,cap_syslog=ep" perf
> +   # setcap -v "cap_sys_admin,cap_sys_ptrace,cap_syslog=ep" perf
> +   perf: OK
> +   # getcap perf
> +   perf = cap_sys_ptrace,cap_sys_admin,cap_syslog+ep
> +
> +As a result, members of perf_users group are capable of conducting performance
> +monitoring by using functionality of the configured Perf tool executable that,
> +when executes, passes perf_events subsystem *scope* checks.
> +
> +This specific *access* control management is only available to superuser or root

Why the *emphasis* here?  We prefer to minimize this kind of markup
whenever possible.

Thanks,

jon